The present invention relates to a technique for use in controlling the spray profile of fuel injected from a fuel injection valve of the type used for an internal combustion engine.
In comparison with a suction pipe injection system where fuel is injected into the suction pipe of an engine, a direct injection system is known wherein fuel is injected directly into the combustion chamber.
A gasoline engine using a direct injection system like this (hereinafter called a direct injection type engine) is described in Japanese Application Patent Laid-Open Publication No. Hei 06-146886, which also discloses a method of improving the fuel consumption. The engine system described in this publication is so constructed that a tumble suction airflow (hereinafter called a tumble airflow) is generated in the combustion chamber by the suction port extending upwards from the suction opening edge, the fuel is injected in the compression stroke, the mixture at a stoichiometric air-fuel ratio is transferred around the ignition plug by the suction airflow, and combustion at a thinner mixture ratio than the stoichiometric air-fuel ratio is realized, thereby to improve the fuel consumption.
Besides, the paper No. F2000A100 of the Seoul 2000 FISITA “World Automotive Congress” describes a direct injection system, in which the opening of the injection hole in an injector is equipped with a step to generate a concentrated spray area and a thin spray area so that the fuel spray is supplied stably to the ignition plug side even when the cylinder pressure is high.
In order to improve the fuel consumption and the exhaust performance of a direct injection type engine, it is desirable to employ a fuel injection valve that provides a spray profile conforming to the size, shape and operating condition of the direct injection type engine.
In the prior art, however, satisfactory consideration has not been given to the technique of controlling the shape of the spray in cross section (that is, in the cross section perpendicular to the axis of the injection hole) including, for example, adjustment of the direction and fuel concentration of the spray flying towards the ignition plug or that of the position and range of a thick area of the fuel spray flying towards the piston side. For this reason, it has been difficult to attain a desired spray profile.